On desktop computers, text is usually entered by typing on physical keyboards that roughly generate one character on the press of a key. The keyboard layout determines which character is generated by the press of which key. Prominent examples are the QWERTY layout and the Dvorak Standard Keyboard Layout, DSK. The alphabetic part of a conventional keyboard is divided into three rows: a top row, a home row and a bottom row. Letter keys, when pressed, produce textual input, usually a lowercase letter. Modifier keys are designated keys on the keyboard that modify the input in some predetermined way. For example, the Shift modifier, when pressed together with a letter key, usually produces an uppercase letter, rather than a lowercase latter. The Alt modifier may produce letters of an alternative alphabet (e.g. Greek instead of Latin), graphical or mathematical symbols, and other kinds of symbolic input. Touch typing refers to a technique of typing that systematically deploys 9-10 fingers at once and enables eyes-free typing, i.e. entering text without having to look at the keyboard.
Touch panels are often integrated into display screens and interpret touches of a user, thus generating information that can be processed by a software and electronic circuit of a computing device. Multi-touch refers to the property of such a touch panel to interpret and distinguish multiple separate touches, e.g. from several fingers, simultaneously.
In mobile computing devices with touch panels, such as smartphones and tablet computers, low text entry rates are a recognized interaction bottleneck. In state of the art devices, separate touches can be robustly detected and distinguished from each other, and the parameters of each touch are cleanly reported to software components, which interpret them. On touch aware mobile devices, text is usually entered as the user presses virtual buttons that are drawn on the screen, so that they resemble a miniature keyboard, which is commonly called virtual keyboard or on-screen keyboard, as the operating surface is also the touch panel. Virtual keyboards commonly sport the QWERTY keyboard layout. Typing on such software keyboards typically suffers from slow entry rates, high error rates and provides a generally tedious and frustrating experience.
Mobile computing devices, such as large smartphones and tablet computers are typically equipped with a multi-touch capable display unit, which enables text entry directly on the screen of the display unit. Several studies have shown that such devices are primarily used for data consumption, such as web browsing, consuming digital media or gaming. For productive use cases, users generally turn to laptop or desktop computers. One of the reasons to this appears to be the difficulty to enter text on such mobile devices. While a user tends to hold a tablet computer by firmly clasping it along its lateral edges to look at the screen of the device, this position is in general ill-suited for on-screen text entry. To enter text, the device typically has to be brought into a stable position, which enables the fingers of both hands to touch the screen. The screen is used to display both an on-screen software keyboard, and the application into which the text should be entered. Such as setup reduces the effective size of the screen that is available for displaying the application.
It is known to use peripheral external keyboard devices that connect to a mobile computing device. Such peripheral devices connect for example by Universal Serial Bus, USB, or wireless channels, such as Bluetooth™ technology. While the use of an external keyboard allows for efficient text entry into tablet computers, it breaks the mobile form factor.
It is known to attach a physical keyboard to the back of a mobile computing device. This allows a user to hold the computing device with both hands and to use the keyboard with the fingers that would usually rest on the rear face of the device. The rows of a typical desktop keyboard are split and located on the left and right parts of the rear face of the mobile computing device. The finger-to-key mapping of a regular desktop keyboard is maintained by the arrangement of such a folded keyboard. However, the form factor of the device is significantly altered, learning to use such a keyboard is often hard, as the user has to adapt to the input device. To our knowledge, all of the known text entry solutions that retain the mobile form factor of a mobile computing device, exhibit typing rates, even after prolonged learning phases, that are significantly lower than the typing rates achieved by trained typist on traditional desktop keyboards, which are of the order of 50-60 words per minute, wpm.